1. Department of Chemistry, University of Florence, via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy, Unitech Pharmaceuticals Inc., 4220A Varsity Drive, Ann Arbor, Michigan 48108, and Institute of Crystallography, Sezione di Monterotondo, Area della Ricerca di Roma, CNR CP10, 00016 Monterotondo Stazione, Rome, Italy